Articulated slip ram for tapered coiled tubing

ABSTRACT

An articulated slip for a slip ram includes a plurality of articulated linked segments, attached to vertical pins or axles which are parallel to the axis of a coiled tubing, for rotatable movement of the linked segments. The articulated linked segments are concave for abutting contact with a tubular through the slip ram. The pins are mounted to a slip ram, which comprises a piston within a cylinder, in the conventional manner for a blowout preventer (BOP) ram. When the slip ram is actuated, the ram moves forward, wrapping the articulated elements around coiled tubing in a gripping motion, much like the fingers of a human hand.

[0001] This application claims the benefit of U.S. Provisional Application Ser. No. 60/421,986 filed Oct. 29, 2002.

FIELD OF THE INVENTION

[0002] The present invention relates generally to the field of blowout preventers for tubing, and, more particularly, to a slip ram in a blowout preventer adapted to accommodate tubing which tapers or otherwise varies in its outside diameter.

BACKGROUND OF THE INVENTION

[0003] The use of blowout preventers in drilling, completion, workover, and production of oil and gas wells is well known. Such blowout preventers generally include a housing with a bore extending through the housing. Opposed chambers extend laterally on either side of the bore in the housing and communicate with the bore. Rams within the chambers are connected to rods that are supported for moving the rams inwardly into the bore to close off the bore. This action divides the bore into a zone above the rams and a zone below the rams. The rods also serve to retract outwardly from the bore to open the bore.

[0004] Various types of rams may be employed such as those which engage circumferentially around a pipe or tubular member for sealing engagement with the tube or pipe, while others are provided with cutting surfaces for shearing tubular members or cables which extend through the bore of the blowout preventer.

[0005] Blowout preventers (BOPs) are also commonly used in coiled tubing systems. Such BOPs provide a means of holding the tubing and isolating the well bore pressure during a variety of conditions, including emergencies. The configuration of the BOP rams and sideport facility allows well-control operations to be conducted under a variety of conditions.

[0006] Newer blowout preventers include four sets of rams, which may be referred to herein as a “Quad BOP”. The system comprises a set of four stacked elements, each with a different function. Blind rams are shut when there is no tubing or tool string extending through the body of the BOP. Shear rams are designed to close on and cut through the tubing. Slip rams close on and hold the tubing, ideally without damaging the surface of the piping or other tubular member. Finally, pipe rams seal around the tubing when it is in place. Each of the rams should only be actuated when the tubing is stationary; otherwise, damage to either the BOP or the tubing is likely. Of the four types of rams just described, the present invention is directed to the slip ram type for use with tubing.

[0007] As previously explained, a slip ram closes onto a tubular, and in the case of the present invention, closes on and holds tubing. Slip segments to grip and suspend coiled tubing are well known and widely used in coiled tubing applications. The slips are typically installed in a set of rams. The slips are most often made in two pieces, one piece in each ram, with gripper teeth on the semi circle resulting in near 360° coverage of the coiled tubing diameter. The gripper section is machined to a specific inside diameter to match the outside diameter of the coiled tubing. This system works reasonably well as long as the coiled tubing is of a constant diameter. Over-worked coiled tubing may become undersized, oversized, or out of round, all of which reduce, or negate the effectiveness of the slip segment gripper teeth.

[0008] Furthermore, recent innovations have provided tubing which has a substantially constant inside diameter, but a substantially constantly increasing outside diameter, so that the tubing presents a tapered aspect in its outside diameter. Development of such a tapered outside diameter coiled tubing renders the gripping system with a set diameter unworkable. In other words, with a first length of tubing through the slip ram, a relatively small diameter of tubing must be accommodated by the slip ram. However, with a longer length of tubing down hole, a larger diameter of tubing must be grasped and held. Current structures of slip rams offer a set diameter of the ram, provided in equal halves on either side of the tubular, and this is incapable of accommodating the varying diameter of tubing which is presented to the slip ram, if the outside diameter of the tubing varies with length. It is believed that the prior art has failed to solve, or even address this problem.

SUMMARY OF THE INVENTION

[0009] The present invention addresses these and other needs and drawbacks in the prior art by providing a slip and a method of gripping tubing having a varying outside diameter. The slip is configured to be retrofitted on existing slip rams in the field so save on costs, and to accommodate such varying diameter tubing when called for by a specific job.

[0010] In a first aspect, the present invention comprises an articulated slip for a slip ram. The slip includes a plurality of articulated elements, attached to vertical pins or axles which are parallel to the axis of the tubular, for rotatable movement. The articulated elements are concave for abutting contact with a tubular through the slip ram. The pins around mounted to a slip ram, which comprises a piston within a cylinder, in the conventional manner for a blowout preventer (BOP) ram. When the slip ram is actuated, the ram moves forward, wrapping the articulated elements around the tubular in a gripping motion, much like the fingers of a human hand.

[0011] The present invention provides a further innovation, other than providing a slip which can grasp a tubular with a varying outside diameter or out of round diameter, and that innovation deals with the irregular surface within the ram itself which contacts the tubing. Although slip rams ideally do not damage the tubing surface of the tubular member through the BOP, it has been found that even a single actuation of the slips against the tubing can score the exterior surface of the tubing. In today's high performance operations at elevated pressures, this scoring can reduce the useful lifetime of the tubular member, particularly with coiled tubing. The interior surface of slips commonly in use today comprises a series of parallel horizontal toothed surfaces, or a series of threads in a substantially horizontal orientation, to contact the tubular and prevent vertical, i.e. axial movement of the tubular. The present invention is further directed to reducing the scoring on the outside surface of the tubular by the slips when engaging and disengaging.

[0012] Thus, in another aspect of the invention, a method of retaining a tapered tubular within a well bore is provided, wherein an articulated slip is impressed upon the tubular by wrapping the slip around the tapered tubular, the extent of closure of the slip determined solely by the outside diameter of the tubular. In a still further aspect of the invention, a cast or molded slip surface comprises a plurality of cleats defining a conical aspect up to a substantially spherical apex of the cone, in order to develop point loading of the cleats on the outside surface of the tubular, rather than the scoring action of linear lands of threads on the surface of the slip, as common in the art.

[0013] These and other features and advantages of this invention will be readily apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, more particular description of the invention, briefly summarized above, may be had by reference to embodiments thereof which are illustrated in the appended drawings.

[0015]FIG. 1 is an elevation section view of an actuator and coiled tubing slip ram constructed in accordance with the teachings of the present invention.

[0016]FIG. 2 is a top view, in partial section, of a set of slips, i.e. from both sides of a tubular, of the present invention.

[0017]FIG. 3 is a front elevation view, i.e. toward an actuator, of the slip of this invention.

[0018]FIG. 3A is a top section taken along section lines A-A of FIG. 3.

[0019]FIG. 3B is a side section view taken along section lines B-B of FIG. 3.

[0020]FIG. 3C is a side section view taken along section lines C-C of FIG. 3.

[0021]FIG. 4A is a top view of a set of linked segments in an actuated position, i.e. positioned against a coiled tubing.

[0022]FIG. 4B is a top view of the linked segments in a retracted position.

[0023]FIG. 5 is a perspective view of a first type of contact surface for a segment.

[0024]FIG. 6A is a top view of a segment of FIG. 5.

[0025]FIG. 6B is a side section view of the segment of FIG. 6A.

[0026]FIG. 7A is a top view of a segment having a second, low stress contact surface.

[0027]FIG. 7B is a side section view of the segment of FIG. 7A.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0028]FIG. 1 illustrates the slip of the present invention in its intended environment. An actuator 10 includes a cylinder body 12 enclosing a cylinder chamber 14 having a piston 16 therein. A close port 18 directs hydraulic fluid pressure to one side of the piston to close the ram, and an open port 20 directs hydraulic fluid pressure to the other side of the piston to open the ram. The piston 16 connects to a rod 22 which terminates at a flange 24 which connects to a slip 26 of this invention, shown and described below in greater detail.

[0029] The slip 26 moves within a body 28 of a blowout preventer which is aligned along a center axis 30. It is to be understood that a similar slip (not shown in FIG. 1) is positioned opposite the slip 26 to enclose a coiled tubing 32 passing through the blowout preventer. Upon actuation, the slip 26 closes in around the coiled tubing 32 in a manner to be described below.

[0030]FIG. 2 illustrates a complementary set of slips 26 and 26′. In the following description, the components of the slip 26 will be described and it is to be understood that the slip 26′ includes the same structure. The flange 24 (FIG. 1) mounts within a flange cavity 34 to move the slip by way of the actuator. The slip includes a slip body 36 to which are attached a first arm 38 and a second arm 40. The arms 38 and 40 are mounted to the body with vertical pins 42 and 44, also as shown in FIG. 3C. The arms 38 and 40 are also pinned at their opposite ends by pins 46 and 48 to a stack of overlapping, articulated linked segments 50. The linked segments are shown in FIG. 2 in the actuated position, in contact with the coiled tubing 32 centered on the axis 30.

[0031] Note also the positioning of a set of articulated segments 70, 72, and 74 for ease of explanation of FIGS. 4A and 4B, described below.

[0032]FIG. 3 shows a front elevation view of the stack of linked segments 50. Each such segment has an arcuate interior surface 52 (See FIG. 5) adapted to grip the outside surface of the coiled tubing 32. The segments are offset from one row to the next, much as bricks are offset in the construction of a brick wall. As shown in FIG. 3A, the pin 48 couples a segment 54 to the arm 40, and the segment 54 also includes a pin 56. A segment 58 is adjacent the segment 54 on the same layer, and includes pins 60 and 62 for rotational movement therewith. A segment 64 (See also FIG. 3B), located below the segments 54 and 58, is pinned to the pin 56 of segment 54 and the pin 62 of segment 58, and thus is articulated in respect of these segments. The other segments are similarly offset, from one layer to the next, down the stack.

[0033] The stacking of the respective linked segments is also illustrated in FIG. 3B. Each of the alternating layers overlaps the layer above and below it (except of course for the top and bottom layers), to provide full diameter contact between the surfaces 52 and the coiled tubing.

[0034] The slip body also includes line guides 66 on either side of the body for mating engagement with the opposite slip body. The slip body may preferably include a line guide on the bottom of the body, and a similar line guide on the top of the body.

[0035]FIGS. 4A and 4B illustrate the actuation of the linked segments, from a retracted position, as shown in FIG. 4B, to a closed position, as shown in FIG. 4A. The arms 38 and 40 (FIG. 2) are moved forward toward the axis 30, thereby moving the pins 46 and 48 forward as well, and the articulated segments, linked together, collapse around the coiled tubing 32.

[0036]FIGS. 5, 6A, and 6B depict a first embodiment of a segment 80 having the arcuate interior surface 52. The surface 52 if preferably formed of substantially horizontal threads 72 (FIG. 6B) with vertical channels 74 cut through the threads to clear debris from the threads 72 and to avoid a continuous stress riser around the tubing. This arrangement somewhat resembles the interior surface of conventional slips, known in the art.

[0037] However, FIGS. 7A and 7B illustrate a new interior surface 82 of the presently preferred mode of the invention. The surface 82 preferably includes a plurality of molded cones 84 or cleats, each of the cones having a rounded apex, in order to properly grip the coiled tubing, while eliminating the scoring action of the threads of the embodiment of FIGS. 6A and 6B.

[0038] It should also be apparent to those skilled in the art that the present invention may find application in other operations requiring the gripping of coiled tubing which may not have uniform outer diameter. For example, the variable diameter, articulated gripper of this invention may be used in a coiled tubing injector, which requires the temporary gripping of the coiled tubing as it is injected into and withdrawn from the borehole.

[0039] The principles, preferred embodiment, and mode of operation of the present invention have been described in the foregoing specification. This invention is not to be construed as limited to the particular forms disclosed, since these are regarded as illustrative rather than restrictive. Moreover, variations and changes may be made by those skilled in the art without departing from the spirit of the invention. 

I claim:
 1. A slip comprising: a. a slip body; b. arms extending from the slip body; c. a first set of vertical pins attaching the arms to the slip body; d. a plurality of linked segments coupled to the arms; and e. a second set of vertical pins linking the segments in overlapping layers.
 2. The slip of claim 1, wherein each of the linked segments defines an arcuate interior surface.
 3. The slip of claim 2, wherein the arcuate interior surface defines threads.
 4. The slip of claim 2, wherein the arcuate interior surface includes a plurality of outwardly extending cones adapted to grip the surface of a tubular.
 5. A slip ram comprising: a. a body having a vertical bore defining a vertical centerline and a horizontal bore extending laterally from the vertical bore; b. a cylinder extending from the horizontal bore; c. a piston within the cylinder; d. a piston rod extending from the piston; and e. a slip coupled to the piston rod within the horizontal bore, the slip comprising i. a slip body; ii. arms extending from the slip body; iii. a first set of vertical pins attaching the arms to the slip body; iv. a plurality of linked segments coupled to the arms; and v. a second set of vertical pins linking the segments.
 6. The slip of claim 5, wherein each of the linked segments defines an arcuate interior surface.
 7. The slip of claim 6, wherein the arcuate interior surface defines threads.
 8. The slip of claim 6, wherein the arcuate interior surface includes a plurality of outwardly extending cones adapted to grip the surface of a tubular. 